1. Keep,reserve,retain,withhold refer to having and holding in possession. Keep (a common word) and retain (a more formal one) agree in meaning to continue to have or hold, as opposed to losing, parting with, or giving up: to keep a book for a week.To reserve is to keep for some future use, occasion, or recipient, or to hold back for a time: to reserve judgment.To withhold is generally to hold back altogether: to withhold help.6. preserve. 8. detain, confine. 41. donjon, dungeon, stronghold.

keep

v.

late Old English cepan "to seize, hold," also "to observe," from Proto-Germanic *kopijanan, but with no certain connection to other languages. It possibly is related to Old English capian "to look," from Proto-Germanic *kap- (cepan was used c.1000 to render Latin observare), which would make the basic sense "to keep an eye on."

The word prob. belongs primarily to the vulgar and non-literary stratum of the language; but it comes up suddenly into literary use c.1000, and that in many senses, indicating considerable previous development. [OED]

Sense of "preserve, maintain" is from mid-14c. Meaning "to maintain in proper order" is from 1550s; meaning "financially support and privately control" (usually in reference to mistresses) is from 1540s. Related: Kept; keeping.

keep

n.

mid-13c., "care or heed in watching," from keep (v.). Meaning "innermost stronghold of a tower" is from 1580s, perhaps a translation of Italian tenazza, with a notion of "that which keeps" (someone or something); the sense of "food required to keep a person or animal" is attested from 1801. For keeps "completely, for good" is American English colloquial, from 1861.